Walrus
The walrus (Odobenus rosmarus) is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies:[1] the Atlantic walrus (O. rosmarus rosmarus) which lives in the Atlantic Ocean, the Pacific walrus (O. rosmarus divergens) which lives in the Pacific Ocean, and O. rosmarus laptevi, which lives in the Laptev Sea. The walrus is immediately recognized by its prominent tusks, whiskers and great bulk. Adult Pacific males can weigh up to 1,700 kilograms (3,700 lb)[3] and, among pinnipeds, are exceeded in size only by the two species of elephant seals.[4] It resides primarily in shallow oceanic shelf habitat, spending a significant proportion of its life on sea ice in pursuit of its preferred diet of benthic bivalve mollusks. It is a relatively long-lived, social animal and is considered a keystone species in Arctic marine ecosystems. The walrus has played a prominent role in the cultures of many indigenous Arctic peoples, who have hunted the walrus for its meat, fat, skin, tusks and bone.[citation needed] In the 19th and early 20th centuries, the walrus was the object of heavy commercial exploitation for blubber and ivory and its numbers declined rapidly. Its global population has since rebounded, though the Atlantic and Laptev populations remain fragmented and at historically depressed levels Description While isolated Pacific males can weigh as much as 2,000 kg (4,400 lb), most weigh between 800 and 1,800 kg (1,800 and 4,000 lb). Females weigh about two-thirds as much, sometimes as little as 400 kg (880 lbs).[17] the Atlantic subspecies weighs about 10–20% less than the Pacific subspecies.[4] The Atlantic Walrus also tends to have relatively shorter tusks and somewhat more flattened snout. Length ranges from 2.2 to 3.6 m (7.2–12 ft).[18] It is the second largest pinniped, after the elephant seals. The walrus' body shape shares features with both sea lions (eared seals: Otariidae) and seals (true seals: Phocidae). As with otariids, it can turn its rear flippers forward and move on all fours; however, its swimming technique is more like that of true seals, relying less on flippers and more on sinuous whole body movements.[4] Also like phocids, it lacks external ears. http://en.wikipedia.org/w/index.php?title=Walrus&action=edit&section=4 edit Tusks and dentition The most prominent feature of the walrus is its long tusks. These are elongated canines, which are present in both sexes and can reach a length of 1 metre (3 ft 3 in) and weigh up to 5.4 kilograms (12 lb).[19] Tusks are slightly longer and thicker among males, who use them for fighting, dominance and display; the strongest males with the largest tusks typically dominate social groups. Tusks are also used to form and maintain holes in the ice and aid the walrus in climbing out of water onto ice.[20] It was previously assumed that tusks were used to dig out prey from the seabed, but analyses of abrasion patterns on the tusks indicate that they are dragged through the sediment while the upper edge of the snout is used for digging.[21] While the dentition of walruses is highly variable, they generally have relatively few teeth other than the tusks. The maximal number of teeth is 38 with dentition formula: , but over half of the teeth are rudimentary and occur with less than 50% frequency, such that a typical dentition includes only 18 teeth [4] http://en.wikipedia.org/w/index.php?title=Walrus&action=edit&section=5 edit Vibrissae Surrounding the tusks is a broad mat of stiff bristles ('mystacial vibrissae'), giving the walrus a characteristic whiskered appearance. There can be 400 to 700 vibrissae in 13 to 15 rows reaching 30 centimetres (12 in) in length, though in the wild they are often worn to a much shorter length due to constant use in foraging.[22] The vibrissae are attached to muscles and are supplied with blood and nerves making them a highly sensitive organ capable of differentiating shapes 3 mm (0.12 in) thick and 2 mm (0.079 in) wide.[22] http://en.wikipedia.org/w/index.php?title=Walrus&action=edit&section=6 edit Skin Aside from the vibrissae, the walrus is sparsely covered with fur and appears bald. Its skin is highly wrinkled and thick, up to 10 cm (3.9 in) around the neck and shoulders of males. The blubber layer beneath is up to 15 cm (5.9 in) thick. Young walruses are deep brown and grow paler and more cinnamon-colored as they age. Old males, in particular, become nearly pink. Because skin blood vessels constrict in cold water, the walrus can appear almost white when swimming. As a secondary sexual characteristic, males also acquire significant nodules, called bosses, particularly around the neck and shoulders.[20] The walrus has an air sac under its throat which acts like a floatation bubble and allows it to bob vertically in the water and sleep. Category:Animals Category:Artic Animals Category:Vertebrates Category:Omnivores Category:Semi-aquatic animals Category:Pinnipeds Category:Water Animals